TRANSACTIONS OF SECTION H. 787 



cortex of the humau train, a third division — the association centres — is to he 

 distinguished. 



If we compare the cerehrum in man and the apes, we find those convolutions 

 •which constitute the motor and sensory centres distinctly marked in both. An ape, 

 like a man, can see, hear, taste, smell and touch ; it also exhibits great muscular 

 activity and variety of movement. It possesses, therefore, similar fundamental 

 centres of sensation and motion, which are situated in areas of the cortex, resembling 

 in arrangement and relative position, though much smaller in size than, the corre- 

 sponding convolutions in the adult human brain. It is not unlikely, though the 

 subject needs additional research, that the minute structure of these centres 

 resembles that of man, though, from the comparatively restricted area of grey 

 matter in the ape, the neui-ones will necessarily be much fewer in number. 



In the cerebrum of a new-born infant, whilst the motor and sensory convolu- 

 tions are distinct, the convolutions for the association areas, though present, are 

 comparatively simple, and do not possess as many windings as are to be seen in 

 the brain of a chimpanzee not more than three or four years old. 



Again, if we compare the brain of the Bushwoman, miscalled the Hottentot 

 Venus, figured by Gratiolet and by Bischoff", or the one studied by Mr. John Marshall, 

 with that of the philosopher Gauss, figured by Rudolph Wagner, we also recognise 

 the convolutions in which the motor and sensory areas are situated. In all these 

 brains they have a comparative simplicity of form and arrangement which enables 

 one readily to discriminate them. When we turn, however, to the associatioii 

 areas in the three tiers of convolutions in the frontal lobe, and in the parieto- 

 occipital and occipito-temporal regions where the bridging or annectant convolu- 

 tions are placed, we cannot fail to observe that in a highly-developed brain, like 

 that of Gauss, the association convolutions have a complexity in arrangement, and 

 an extent of cortical surface much more marked than in the Bushwoman, and to 

 a still greater degree than in the ape. The naked-eye anatomy of the brain there- 

 fore obviously points to the conclusion that these association areas are of great 

 physiological importance. 



The problem which has now to be solved is the determination of their function. 

 Prolonged investigation into the development and comparative histology of the 

 brain will be necessary before we can reach a sound anatomical basis on which to 

 found satisfactory conclusions. It will especially be necessary to study the suc- 

 cessive periods of development of the nerve-fibre tracts in the cerebrum of apes and 

 other mammals, as well as the magnitude and intimate structure of the association 

 areas in relation to that of the motor and sensory areas in the same species. 



Flechsig, however, has not hesitated to ascribe to the association centres func- 

 tions of the highest order. He believes them to be parts of the cerebral cortex 

 engaged in the manifestations of the higher intelligence, such as memory, judgment, 

 and reflection ; but in the present state of our knowledge such conclusions are of 

 course quite speculative. 



It is not unlikely, however, that the impulses which are conveyed by the inter- 

 mediate nerve-tracts, either on the one hand, from the sense centres to the associa- 

 tion centres, or on the other, from the association centres to the sensory and motor 

 centres, are neither motor nor sensory impulses, but a form of nerve energy, 

 determined by the terminal connections and contacts of the nerve fibres. It is possible 

 that the association centres, with the intermediate connecting tracts, may serve to 

 harmonise and control the centres for the reception of sensory impressions that 

 we translate into consciousness, with those which excite motor activity, so as to 

 give to the brain a completeness and perfection of structural mechanism, which 

 without them it could not have possessed. 



We know that an animal is guided by its instincts, through which it provides 

 for its individual wants, and fulfils its place in nature. In man, on the other 

 hand, the instinctive acts are under the influence of the reason and intelligence, 

 and it is possible that the association centres, with the intermediate association 

 fibres which connect them with the sensory and motor centres, may be the 

 mechanism through which man is enabled to control his animal instincts, so far as 

 they are dependent on motion and sensation. 



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